Free space optical (FSO) communications systems are wireless point-to-point communications systems that use lasers to transmit and receive communication signals via line-of-sight directed laser beams. Because the beams are directed and narrow, FSO communications systems are generally thought to be secure and reliable. The beams can be sufficiently low-powered to reduce a risk of eye injuries. An FSO system that switches power levels is disclosed in U.S. Pat. No. 5,229,593, for example.
FSO communications systems have proved to be especially advantageous in campus environments. For example, a business organization may wish to construct a local area network (LAN) linking employees located in different nearby buildings. If the organization were to rely on installing private dedicated lines using, for example, fiber optic cable, it would incur considerable expense in terms of construction costs for installing the cables, as well as the inevitable delay in establishing the LAN until construction could be completed. The costs and delay would likely be even greater were the campus located within an urban setting, where even linking employees in buildings located just across the street from one another can require extensive regulatory approvals and expensive disruptions to local activity. Such delays and/or disruption may be particularly acute in historical districts or protected wildlife areas, for example.
An FSO communication system provides an effective and efficient alternative because the communications link can be established simply by deploying the necessary low-powered laser transceivers in or around the buildings (e.g., on rooftops or in windows) or at other sites to be linked. Often, an FSO communication system can be deployed within as little as 24 hours, and no government licensing is typically required. The FSO communications system can carry voice, video, and data signals or combinations thereof at a very high rate. The FSO communications system also can serve as an organization's single link to the Internet, as well as provide for streaming media, video conferencing, and on-line collaboration among organization members dispersed throughout a campus.
One significant drawback of an FSO communications system, however, is its possible vulnerability to atmospheric disturbances. Precipitation, heavy fog, low cloud cover, and even smog are among the various atmospheric disturbances that can impede transmission and receipt of FSO communications systems line-of-sight signals. To date, various providers of FSO communications systems have attempted to compensate for this drawback by relying on radio frequency (RF)/microwave back-up systems for redundancy.
Among various FSO communications systems providers, such as LightPointe, Inc., fSONA Communications Corp., Optical Access, Inc., and Furtera, Inc., many if not most have opted for similar RF back-up system for possible disruptions to an FSO communications system. LightPointe, Inc., for example, recommends complementing an FSO communications system with a microwave radio back-up to provide network redundancy. Furtera, Inc., similarly recommends a hybrid system combining free space optics with RF capabilities.
These RF/microwave redundant systems pose their own problems, however, in terms of increased cost and complexity. The purchase and installation of a separate back-up system offsets the reduced-cost and easy installation provided by the FSO communications system. Moreover, once such an RF/microwave redundant system is installed, it remains idle unless and until there is a disruption in the FSO communication system. Moreover, even if the redundant system remains idle, there nonetheless are costs associated with maintaining the system in working order. Thus, these costs further offset the efficiency advantages of conventional FSO-based communication system.